Chapter 28 Gastrointestinal Infections

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Chapter 28 Gastrointestinal Infections Food
Poisoning

• MLAB 2434 Clinical Microbiology
• Cecile Sanders Keri Brophy-Martinez

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General Concepts

• A complete history should be taken
• Foods eaten recently
• Exposure to ill patients
• Recent travel
• Any underlying illnesses
• Diarrhea may be caused by viruses, bacteria, food
  poisoning and non-infectious processes

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Anatomy of GI Tract

• Organisms must be able to survive gastric acids
  in order to reach the small bowel
• In small bowel, motility is major host defense
• Generally, a large dose of organisms is needed to
  cause disease

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Normal GI Flora

• Stomach contains few organisms
• Upper part of small bowel contains small numbers
  of Enterococcus sp, lactobacilli, and
  diphtheroids, along with Candida albicans in
  20-40 of individuals
• Colon contains large numbers of anaerobes and
  facultative anaerobes in 10001 ratio
• Colon produces IgA
• Pathogens would have to compete with normal flora

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Diagnosing Cause of Diarrhea

• History
• Travel to endemic areas of world
• Food
• Page 950 has list of foods with typical pathogens
• Physical Exam
• Dehydration
• Toxic megacolon
• Intestinal rupture

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Common Bacterial Agents Causing Diarrhea

• See list on page 953
• Campylobacter jejuni
• Most common cause of bacterial diarrhea in U.S.
• Inadequately cooked poultry, untreated water,
  unpasteurized milk, and exposure to animals with
  diarrhea
• Self-limiting

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Common Bacterial Agents Causing Diarrhea (contd)

• Campylobacter jejuni (contd)
• Grows best at 42 degrees C
• Microaerophilic conditions
• Campy plate
• Gram-negative curved rods, seagull wings

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Common Bacterial Agents Causing Diarrhea (contd)

• Salmonella species
• Gastroenteritis and Food Poisoning
• Contracted by eating undercooked meat, poultry,
  eggs, and contaminated dairy products
• Nausea, vomiting, and diarrhea
• Usually self-limiting antibiotics discouraged
  because they can induce carrier state

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Common Bacterial Agents Causing Diarrhea (contd)

• Salmonella species (contd)
• Enteric Fever
• Typhoid fever is most severe
• S. typhi, Salmonella serotype A, Salmonella
  serotype choleraesuis, and other serotypes
• Contaminated food and water
• Organisms invade small bowel colonic tissue
• Live and reproduce in monocytes
• Can invade gall bladder and produce carrier
  state

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Common Bacterial Agents Causing Diarrhea (contd)

• Salmonella species (contd)
• Bacteremia
• S. typhimurium, S. paratyphi A and B, and S.
  choleraesuis
• Shigella species
• Diarrhea may have blood
• Invades mucosa with intense inflammatory response
• Most communicable of the diarrheal bacteria

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Common Bacterial Agents Causing Diarrhea (contd)

• Diarrheogenic Escherichia coli
• Vibrio species
• Yersinia enterocolitica
• Clostridium difficle
• Listeria monocytogenes

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Common Bacterial Agents Causing Diarrhea (contd)

• Many cases of food poisoning caused by toxins
  produced by bacteria
• Bacteria may no longer be alive, but toxins can
  cause food poisoning
• Example Staph

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Laboratory Diagnosis of Gastrointestinal Pathogens

• Specimen Collection and Handling
• Stool should be processed ASAP NOT refrigerated
• Direct microscopic exam almost exclusively
  performed to detect presence of WBCs and RBCs

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Laboratory Diagnosis of Gastrointestinal
Pathogens (contd)

• Stool Cultures
• Must use a variety of selective media (extensive
  list on page 964)

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Treatment of Diarrhea

• Patients must be watched for dehydration
• Antibiotics are NOT effective against viral
  pathogens
• Antibiotics may shorten illness by invasive
  bacteria or an enterotoxin-mediated process
• Antidiarrheal mediations (Lomotil, Pepto-Bismol)
• Prophylactic therapy not recommended for
  travelers
• When traveling, Boil it, peel it, cook it, or
  forget it!